CN113817216A - Polyimide nanofiber aerogel and preparation method thereof - Google Patents
Polyimide nanofiber aerogel and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a preparation method of a fused micro-crosslinked Polyimide (PI) nanofiber aerogel. The aerogel adopts polyimide nanofiber as a skeleton material of the aerogel, and the preparation steps are as follows: polyanhydride and polyamine are subjected to polycondensation reaction according to equal molar ratio to synthesize a polyamic acid solution, a polyamic acid nanofiber membrane is prepared through electrostatic spinning, then the polyamic acid nanofiber membrane is dispersed in a solvent, the dispersion solution is subjected to freezing crystallization, the crystallization phase is removed through vacuum freezing drying to obtain uncrosslinked polyamic acid nanofiber aerogel, and finally the aerogel is subjected to thermal imidization to prepare the polyimide nanofiber aerogel with a cross-linked skeleton structure support due to the thermal melting property of part of fibers. The polyimide nanofiber aerogel prepared by the invention has the advantages of low density, mechanical flexibility, good compression resilience and low thermal conductivity coefficient, is simple in preparation process and rich in raw material source, and can be used in the fields of heat insulation, flame retardance, adsorption separation, electromagnetic energy storage and the like.
Description
Technical Field
The invention belongs to the technical field of high polymer materials, and particularly relates to a fused micro-crosslinked polyimide nanofiber aerogel and a preparation method thereof.
Background
Aerogel is a nano-scale porous solid material formed by replacing liquid phase in gel with gas by a certain drying way through a sol-gel method. The general preparation method is that a sol-gel method is assisted by a supercritical drying technology, the sol-gel process of a precursor directly influences the construction of a final aerogel three-dimensional network structure so as to directly determine the final performance and functional application of the aerogel material, and the aerogel prepared by the method has a high-density cross-linked network structure and is not beneficial to stress dispersion; in addition, most of the matrixes of the prior aerogel materials are inorganic materials such as silicon dioxide, and the aerogel materials are easy to break due to high brittleness and easy to deliquesce in the using process, so that the aerogel materials with high thermal stability, high flexibility and excellent mechanical properties are urgently needed to be developed, and a certain application value is endowed.
Polyimide is a high-performance polymer with an imide ring structure on a main chain, has the unique advantages of excellent high and low temperature resistance, mechanical property, dielectric property, chemical stability and ultraviolet radiation resistance, and is applied to the high-tech fields of aerospace, microelectronics, atomic energy and the like. In recent years, with the development of electrostatic spinning technology, nanofiber aerogel materials taking polyimide as a matrix are widely concerned, and the materials show great potential application values in the fields of heat preservation and insulation, adsorption separation, sensors, filter materials, electromagnetic shielding and the like due to the combination of the advantages of large specific surface area and high porosity of aerogel and the characteristics of high temperature resistance and chemical stability of polyimide.
However, the polyimide nanofiber aerogel is easy to crack and crack in the preparation process, and in the compression rebound experiment process, the polyimide nanofiber aerogel also has the characteristic of poor rebound, and because only loose physical lap joints exist between skeleton fibers of the polyimide nanofiber aerogel and no specific skeleton connection supporting points exist, the polyimide nanofiber aerogel cannot be restored to the original position due to concentrated stress in the compression process. In order to solve the problems, patent CN 109731533 a provides a polyimide nanofiber aerogel with a cross-linked structure, which is formed by adding a cross-linking agent (polybenzoxazine) into a polyimide nanofiber dispersion liquid, and the aerogel prepared by this kind of method is easy to introduce a third substance, resulting in non-uniformity of the whole aerogel, and the cross-linking agent has a high unit price and is not easy to obtain, which is also a disadvantage that limits its popularization. Therefore, it is a challenging problem in the field to explore a simple and feasible method for constructing a three-dimensional network of polyimide nanofiber aerogel.
The invention prepares the polyimide nanofiber aerogel by combining the technologies of electrostatic spinning, vacuum freeze drying and the like, on one hand, the polyimide nanofiber membrane prepared by electrostatic spinning is used as the matrix material of the aerogel so as to reduce the quality and the density of the aerogel as much as possible and improve the porosity of the aerogel, the thermal conductivity coefficient of the aerogel is close to that of air, the aerogel is endowed with good heat preservation and heat insulation performance, on the other hand, the introduction of the polyimide nanofiber membrane with the hot melting type enables two or more polyimide nanofibers to be mutually connected to form a cross-linked structure in a hot melting state, thus improving the internal microstructure of the polyimide aerogel in loose physical lap joint, reducing the possibility of stress concentration of the aerogel, therefore, the aerogel has good resilience and certain compression flexibility. Meanwhile, the aerogel has good application prospect in the fields of adsorption filtration and the like due to the characteristic of high porosity.
Disclosure of Invention
The invention aims to solve the defects of the prior art and provides a simple and effective process method for preparing the fused micro-crosslinked polyimide nano-fiber aerogel. The method has the advantages of simple process, good flexibility of the aerogel, low thermal conductivity, controllable density of the aerogel and good application prospect.
In order to achieve the purpose, the invention provides the following technical scheme:
1. a polyimide nanofiber aerogel is characterized by comprising more than two polyimide fibers, wherein at least one polyimide fiber is a polyimide fiber which can be thermally melted under high-temperature thermal imidization treatment; the polyimide nanofiber aerogel is characterized in that fusion cross-linking points are formed among fibers; the content of the polyimide fiber thermally meltable under high-temperature thermal imidization treatment is 10 to 50 wt%, preferably 12 to 30 wt%.
Further, the fiber diameter is 100-1000nm, preferably 200-700 nm; the density of the polyimide nanofiber aerogel is 5-50 mg/cm3Preferably 10 to 20mg/cm3(ii) a The contact angle of the water phase is 125-140 degrees, preferably 130-135 degrees; the porosity is 97% or more, preferably 99% or more; the stress at 50% compressive strain is 10 to 100kPa, preferably 30 to 50 kPa.
2. The preparation method of the polyimide nanofiber aerogel according to the technical scheme 1 is characterized by comprising the following steps of:
a: synthesizing a polyamic acid solution;
b: preparing a polyamic acid solution into a polyamic acid nanofiber membrane through electrostatic spinning;
c: dispersing the polyamic acid nanofiber membrane in a solvent to prepare polyamic acid nanofiber dispersion liquid; wherein at least one polyamic acid nanofiber membrane contains polyamic acid fibers which can be thermally fused under high-temperature thermal imidization treatment;
d: freezing and crystallizing the dispersion liquid of more than two kinds of polyamide acid nano fibers to prepare a crystal phase of the dispersion liquid of the polyamide acid nano fibers; removing the crystalline phase of the polyamic acid nanofiber dispersion liquid through vacuum freeze drying to obtain the uncrosslinked polyamic acid nanofiber aerogel;
e: and performing high-temperature thermal imidization treatment on the polyamic acid nanofiber aerogel to obtain the micro-crosslinking polyimide nanofiber aerogel.
Further, the dispersing solvent in the step C is one or more of ethylene glycol, glycerol, tertiary butanol, water, dioxane and phenol; preferably pure tert-butyl alcohol or a 20-30 wt% tert-butyl alcohol aqueous solution.
Further, the heat-fusible polyimide according to step C is characterized in that the heat-fusible polyamide acid fiber subjected to the high-temperature thermal imidization treatment is one or more selected from polyamide acid fiber of a hexafluoro dianhydride (6FDA)/4,4 '-diaminodiphenyl ether (4, 4' -ODA) system, polyamide acid fiber of a 3,3 ', 4, 4' -diphenyl ether tetracarboxylic dianhydride (ODPA)/4,4 '-ODA system, polyamide acid fiber of a bisphenol a dianhydride (BPADA)/4, 4' -ODA system, polyamide acid fiber of a P84 type polyimide precursor, and polyether imide precursor.
Further, pre-freezing the frozen crystal in the step D in a freeze dryer at the low temperature of-10 to-95 ℃, preferably-20 to-90 ℃, wherein the freezing time is 2 to 15 hours, preferably 3 to 10 hours; or performing rapid freezing in the liquid nitrogen atmosphere, wherein the freezing time is 5-40 min, and preferably 10-20 min.
Further, in the step E, the high-temperature thermal imidization treatment is carried out by raising the temperature from room temperature to 130-160 ℃, preferably 135 ℃, and keeping the temperature for 0.1-2 hours, preferably 0.3-1 hour, and most preferably 0.5 hour; then heating to 200-400 ℃, preferably 300-350 ℃, and preserving heat for 0.1-2 h, preferably 0.3-1 h, and most preferably 0.5 h; the heating rate is 1-5 ℃/min, preferably 2-3 ℃/min.
Compared with the prior art, the invention has the following advantages:
(1) the invention provides a method for preparing polyimide aerogel with high resilience, which has the advantages of simple implementation process, easily-satisfied conditions, simple and convenient steps, easy repetition, no damage to polyimide matrix fibers in the treatment process, simple and green freeze-drying process, wide application range and application in the preparation of polyimide fiber aerogel of all systems;
(2) the polyimide nanofiber aerogel prepared by the method disclosed by the invention is very low in density, has an ultra-large contact angle (in a water phase), has super-hydrophobic performance, and has a wide application prospect in the field of oil-water separation;
(3) the polyimide nanofiber aerogel prepared by the invention has excellent resilience and flexibility, can generate large strain under smaller stress, can automatically recover the volume height before the strain is 70%, and has wide application prospect in the field of adsorption, filtration and separation;
(4) the polyimide nanofiber aerogel prepared by the invention can be automatically subjected to fiber lap joint with fibers of other systems in a flexible hot melting system in the thermal imidization process to form a reliable-support three-dimensional reticular structure, and can eliminate the phenomenon of stress concentration and improve the stability of the structure.
Drawings
FIG. 1 is a schematic external view of a polyimide nanofiber aerogel (example 2) prepared by mixing pyromellitic dianhydride/4, 4 '-diaminodiphenyl ether (PMDA/ODA) with 3, 3', 4,4 '-diphenyl ether tetracarboxylic dianhydride/4, 4' -diaminodiphenyl ether (ODPA/ODA).
FIG. 2 is a schematic external view of a polyimide nanofiber aerogel (example 5) prepared by mixing pyromellitic dianhydride/4, 4 '-diaminodiphenyl ether (PMDA/ODA) with 3, 3', 4,4 '-diphenyl ether tetracarboxylic dianhydride/4, 4' -diaminodiphenyl ether (ODPA/ODA) and bending the same;
FIG. 3 is an SEM topography of pyromellitic dianhydride/4, 4 '-diaminodiphenyl ether (PMDA/ODA) mixed 3, 3', 4,4 '-diphenyl ether tetracarboxylic dianhydride/4, 4' -diaminodiphenyl ether (ODPA/ODA) polyimide nanofiber aerogel (example 3);
FIG. 4 is a graph showing compressive stress-strain curves at different fiber ratios for pyromellitic dianhydride/4, 4 '-diaminodiphenyl ether (PMDA/ODA) mixed with 3, 3', 4,4 '-diphenyl ether tetracarboxylic dianhydride/4, 4' -diaminodiphenyl ether (ODPA/ODA) polyimide nanofiber aerogel (examples 1 to 4);
FIG. 5 is a water contact angle diagram of a hexafluoro dianhydride/4, 4 '-diaminodiphenyl ether (6FDA/ODA) mixed 3, 3', 4,4 '-diphenyl ether tetracarboxylic dianhydride/4, 4' -diaminodiphenyl ether (ODPA/ODA) polyamic acid fiber aerogel (example 3);
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be noted that: the following examples are only for illustrating the present invention and are not intended to limit the technical solutions described in the present invention. Thus, while the present invention has been described in detail with reference to the following examples, it will be understood by those skilled in the art that the present invention may be modified and equivalents may be substituted; all such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.
The invention provides a preparation method of a fused micro-crosslinked polyimide nanofiber aerogel, which comprises the following steps:
example 1
Preparing a polyamic acid fiber membrane of a PMDA-ODA/ODPA-ODA system, dispersing the polyamic acid fiber membrane by a homogenizer, pouring the polyamic acid fiber membrane into a mold, freezing and drying the polyamic acid fiber membrane, and then carrying out thermal imidization on the polyamic acid fiber membrane to obtain the thermal-melting micro-crosslinking polyimide nano-fiber aerogel. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4,4 '-diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30mL of N, N' -Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with a solid content of 12%, mechanically stirring for 2h, filling the polyamic acid solution into a 20mL injector, and preparing a polyamic acid fiber membrane by applying an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 20 kV; spinning temperature: room temperature; spinning humidity: 40 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 80.0 m/min; receiving distance: 20 cm. Will prepare outThe polyamic acid fiber membrane is placed in a super clean bench for 12h, and the polyamic acid fiber membrane of the ODPA-ODA system is prepared by the same method. (2) Uniformly dispersing a polyamic acid fiber membrane of a PMDA-ODA/ODPA-ODA system in an aqueous solution of tert-butyl alcohol by using a homogenizer according to a mass ratio of 6:4, pouring the nanofiber dispersion liquid into a mold with the mass fraction of the polyamic acid fiber being 1 wt%, pre-freezing at-80 ℃ for 8 hours, and performing freeze drying (the vacuum degree is 0-1 Pa, and the drying time is 72 hours) to prepare the polyamic acid nanofiber aerogel. (3) And (2) placing the polyamic acid nanofiber aerogel in a heating furnace, heating the polyamic acid nanofiber aerogel from room temperature to 150 ℃ at the heating rate of 2 ℃/min, and preserving heat for 0.5h, and then heating the polyamic acid nanofiber aerogel to 300 ℃ at the heating rate of 2 ℃/min and preserving heat for 0.5h to obtain the polyimide nanofiber aerogel. The aerogel had a density of 11.52mg/cm3The porosity was 99.08%, the shrinkage was 23.12%, the stress at 50% compressive strain was 43.2kPa, and the contact angle was 132.21 °.
Example 2
Preparing a polyamic acid fiber membrane of a PMDA-ODA/ODPA-ODA system, dispersing the polyamic acid fiber membrane by a homogenizer, pouring the polyamic acid fiber membrane into a mold, freezing and drying the polyamic acid fiber membrane, and then carrying out thermal imidization on the polyamic acid fiber membrane to obtain the thermal-melting micro-crosslinking polyimide nano-fiber aerogel. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4,4 '-diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30mL of N, N' -Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with a solid content of 12%, mechanically stirring for 2h, filling the polyamic acid solution into a 20mL injector, and preparing a polyamic acid fiber membrane by applying an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 20 kV; spinning temperature: room temperature; spinning humidity: 40 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 80.0 m/min; receiving distance: 20 cm. The prepared polyamic acid fiber membrane is placed in a super clean bench for 12h, and the polyamic acid fiber membrane of the ODPA-ODA system is prepared by the same method. (2) Uniformly dispersing the polyamic acid fiber membrane of the PMDA-ODA/ODPA-ODA system in an aqueous solution of tert-butyl alcohol by using a homogenizer according to the mass ratio of 7:3, wherein the mass fraction of the polyamic acid fiberPouring the nanofiber dispersion liquid into a mold for 1 wt%, pre-freezing for 8h at-80 ℃, and performing freeze drying (the vacuum degree is 0-1 Pa, and the drying time is 72h) to obtain the polyamic acid nanofiber aerogel. (3) And (2) placing the polyamic acid nanofiber aerogel in a heating furnace, heating the polyamic acid nanofiber aerogel from room temperature to 150 ℃ at the heating rate of 2 ℃/min, and preserving heat for 0.5h, and then heating the polyamic acid nanofiber aerogel to 300 ℃ at the heating rate of 2 ℃/min and preserving heat for 0.5h to obtain the polyimide nanofiber aerogel. The aerogel had a density of 11.28mg/cm3The porosity was 99.25%, the shrinkage was 18.21%, the stress at 50% compressive strain was 38.2kPa, and the contact angle was 133.15 °.
Example 3
Preparing a polyamic acid fiber membrane of a PMDA-ODA/ODPA-ODA system, dispersing the polyamic acid fiber membrane by a homogenizer, pouring the polyamic acid fiber membrane into a mold, freezing and drying the polyamic acid fiber membrane, and then carrying out thermal imidization on the polyamic acid fiber membrane to obtain the thermal-melting micro-crosslinking polyimide nano-fiber aerogel. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4,4 '-diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30mL of N, N' -Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with a solid content of 12%, mechanically stirring for 2h, filling the polyamic acid solution into a 20mL injector, and preparing a polyamic acid fiber membrane by applying an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 20 kV; spinning temperature: room temperature; spinning humidity: 40 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 80.0 m/min; receiving distance: 20 cm. The prepared polyamic acid fiber membrane is placed in a super clean bench for 12h, and the polyamic acid fiber membrane of the ODPA-ODA system is prepared by the same method. (2) Uniformly dispersing a polyamic acid fiber membrane of a PMDA-ODA/ODPA-ODA system in an aqueous solution of tert-butyl alcohol by using a homogenizer according to a mass ratio of 8:2, pouring the nanofiber dispersion liquid into a mold with the mass fraction of the polyamic acid fiber being 1 wt%, pre-freezing for 8 hours at-80 ℃, and performing freeze drying (the vacuum degree is 0-1 Pa, and the drying time is 72 hours) to prepare the polyamic acid nanofiber aerogel. (3) The polyamic acid nanofiber aerogel is placed in a heating furnace, and the temperature is raised from room temperature to 150 ℃ at the temperature rise speed of 2 ℃/minAnd preserving heat for 0.5h, then heating to 300 ℃ at the heating rate of 2 ℃/min and preserving heat for 0.5h, thereby preparing the polyimide nanofiber aerogel. The aerogel has a density of 10.52mg/cm3The porosity was 99.35%, the shrinkage was 15.12%, the stress at 50% compressive strain was 31.4kPa, and the contact angle was 131.99 °.
Example 4
Preparing a polyamic acid fiber membrane of a PMDA-ODA/ODPA-ODA system, dispersing the polyamic acid fiber membrane by a homogenizer, pouring the polyamic acid fiber membrane into a mold, freezing and drying the polyamic acid fiber membrane, and then carrying out thermal imidization on the polyamic acid fiber membrane to obtain the thermal-melting micro-crosslinking polyimide nano-fiber aerogel. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4,4 '-diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30mL of N, N' -Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with a solid content of 12%, mechanically stirring for 2h, filling the polyamic acid solution into a 20mL injector, and preparing a polyamic acid fiber membrane by applying an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 20 kV; spinning temperature: room temperature; spinning humidity: 40 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 80.0 m/min; receiving distance: 20 cm. The prepared polyamic acid fiber membrane is placed in a super clean bench for 12h, and the polyamic acid fiber membrane of the ODPA-ODA system is prepared by the same method. (2) Uniformly dispersing a polyamic acid fiber membrane of a PMDA-ODA/ODPA-ODA system in an aqueous solution of tert-butyl alcohol by using a homogenizer according to a mass ratio of 5:5, pouring the nanofiber dispersion liquid into a mold with the mass fraction of the polyamic acid fiber being 1 wt%, pre-freezing at-80 ℃ for 8 hours, and performing freeze drying (the vacuum degree is 0-1 Pa, and the drying time is 72 hours) to prepare the polyamic acid nanofiber aerogel. (3) And (2) placing the polyamic acid nanofiber aerogel in a heating furnace, heating the polyamic acid nanofiber aerogel from room temperature to 150 ℃ at the heating rate of 2 ℃/min, and preserving heat for 0.5h, and then heating the polyamic acid nanofiber aerogel to 300 ℃ at the heating rate of 2 ℃/min and preserving heat for 0.5h to obtain the polyimide nanofiber aerogel. The aerogel has a density of 10.26mg/cm3The porosity was 99.48%, the shrinkage was 13.22%, the stress at 50% compressive strain was 23.2kPa, and the contact angle was 131.52 °。
Example 5
Preparing a polyamic acid fiber membrane of a PMDA-ODA/ODPA-ODA system, dispersing the polyamic acid fiber membrane by a homogenizer, pouring the polyamic acid fiber membrane into a mold, freezing and drying the polyamic acid fiber membrane, and then carrying out thermal imidization on the polyamic acid fiber membrane to obtain the thermal-melting micro-crosslinking polyimide nano-fiber aerogel. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4,4 '-diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30mL of N, N' -Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with a solid content of 12%, mechanically stirring for 2h, filling the polyamic acid solution into a 20mL injector, and preparing a polyamic acid fiber membrane by applying an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 20 kV; spinning temperature: room temperature; spinning humidity: 40 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 80.0 m/min; receiving distance: 20 cm. The prepared polyamic acid fiber membrane is placed in a super clean bench for 12h, and the polyamic acid fiber membrane of the ODPA-ODA system is prepared by the same method. (2) Uniformly dispersing a polyamic acid fiber membrane of a PMDA-ODA/ODPA-ODA system in an aqueous solution of tert-butyl alcohol by using a homogenizer according to a mass ratio of 8:2, pouring the nanofiber dispersion liquid into a mold with the mass fraction of the polyamic acid fiber being 2 wt%, pre-freezing for 8 hours at-80 ℃, and performing freeze drying (the vacuum degree is 0-1 Pa, and the drying time is 72 hours) to prepare the polyamic acid nanofiber aerogel. (3) And (2) placing the polyamic acid nanofiber aerogel in a heating furnace, heating the polyamic acid nanofiber aerogel from room temperature to 150 ℃ at the heating rate of 2 ℃/min, and preserving heat for 0.5h, and then heating the polyamic acid nanofiber aerogel to 300 ℃ at the heating rate of 2 ℃/min and preserving heat for 0.5h to obtain the polyimide nanofiber aerogel. The aerogel has a density of 21.63mg/cm3The porosity was 98.86%, the shrinkage was 15.28%, the stress at 50% compressive strain was 53.26 kPa, and the contact angle was 134.56 °.
Example 6
Preparing a polyamic acid fiber membrane of a PMDA-ODA/6FDA-ODA system, dispersing the polyamic acid fiber membrane by a homogenizer, pouring the polyamic acid fiber membrane into a mold, freezing and drying the mold, and then carrying out thermal imidization to obtain the thermal-melting micro-crosslinking polyimide nano-fiber aerogel. (1) BalanceTaking 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4,4 '-diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30mL of N, N' -Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, filling the polyamic acid solution into a 20mL injector, and preparing the polyamic acid fiber membrane by using an electrostatic spinning technology, wherein the parameters of an electrostatic spinning machine are spinning voltage: 20 kV; spinning temperature: room temperature; spinning humidity: 40 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 80.0 m/min; receiving distance: 20 cm. The prepared polyamic acid fiber membrane is placed in a super clean bench for 12h, and the polyamic acid fiber membrane of a 6FDA-ODA system is prepared by the same method. (2) Uniformly dispersing a polyamic acid fiber membrane of a PMDA-ODA/6FDA-ODA system in an aqueous solution of tert-butyl alcohol by using a homogenizer according to a ratio of 4:1, wherein the mass fraction of the polyamic acid fiber is 1 wt%, pouring the nanofiber dispersion liquid into a mold, pre-freezing at ultralow temperature, and preparing the polyamic acid nanofiber aerogel by a freeze-drying method. (3) And (2) placing the polyamic acid nanofiber aerogel in a heating furnace, heating the polyamic acid nanofiber aerogel from room temperature to 150 ℃ at the heating rate of 2 ℃/min, and preserving heat for 0.5h, and then heating the polyamic acid nanofiber aerogel to 300 ℃ at the heating rate of 2 ℃/min and preserving heat for 0.5h to obtain the polyimide nanofiber aerogel. The aerogel has a density of 12.52mg/cm3The porosity was 99.15%, the shrinkage was 14.23%, the stress at 50% compressive strain was 32.5kPa, and the contact angle was 135.19 °.
Example 7
Preparing a polyamic acid fiber membrane of a PMDA-ODA/P84 system, dispersing the polyamic acid fiber membrane by a homogenizer, pouring the polyamic acid fiber membrane into a mold, freezing and drying the polyamic acid fiber membrane, and then carrying out thermal imidization to obtain the thermal-melting micro-crosslinking polyimide nano-fiber aerogel. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4, 4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving the ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving the ODA in the DMF, adding the PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, filling the polyamic acid solution into a containerIn a 20mL injector, the polyamide acid fiber membrane is prepared by applying an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are the spinning voltage: 20 kV; spinning temperature: room temperature; spinning humidity: 40 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 80.0 m/min; receiving distance: 20 cm. The prepared polyamic acid fiber membrane is placed in an ultra-clean bench for 12h, and the polyamic acid fiber membrane of the P84 system is prepared by the same method. (2) Uniformly dispersing a polyamic acid fiber membrane of a PMDA-ODA/P84 system in an aqueous solution of tert-butyl alcohol by using a homogenizer according to a ratio of 4:1, wherein the mass fraction of the polyamic acid fiber is 1 wt%, pouring the nanofiber dispersion into a mold, pre-freezing at ultralow temperature, and performing freeze drying to obtain the polyamic acid nanofiber aerogel. (3) And (2) placing the polyamic acid nanofiber aerogel in a heating furnace, heating the polyamic acid nanofiber aerogel from room temperature to 150 ℃ at the heating rate of 2 ℃/min, and preserving heat for 0.5h, and then heating the polyamic acid nanofiber aerogel to 300 ℃ at the heating rate of 2 ℃/min and preserving heat for 0.5h to obtain the polyimide nanofiber aerogel. The aerogel has a density of 12.68mg/cm3The porosity was 99.02%, the shrinkage 13.08%, the stress at 50% compressive strain was 29.726 kPa, and the contact angle was 131.25 °.
Example 8
Preparing a polyamic acid fiber membrane of a PMDA-ODA/BPADA-ODA system, dispersing the polyamic acid fiber membrane by a homogenizer, pouring the polyamic acid fiber membrane into a mold, freezing and drying the polyamic acid fiber membrane, and then carrying out thermal imidization to obtain the thermal-melting micro-crosslinking polyimide nano-fiber aerogel. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4, 4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30mL of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, filling the polyamic acid solution into a 20mL injector, and preparing the polyamic acid fiber membrane by using an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 20 kV; spinning temperature: room temperature; spinning humidity: 40 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 80.0 m/min; receiving distance: 20 cm. Placing the prepared polyamic acid fiber membrane in a super clean bench for 12h, and using the same methodThe method prepares the polyamide acid fiber membrane of the BPADA-ODA system. (2) Uniformly dispersing a polyamic acid fiber membrane of a PMDA-ODA/BPADA-ODA system in an aqueous solution of tert-butyl alcohol by using a homogenizer according to a ratio of 9:1, wherein the mass fraction of the polyamic acid fiber is 1 wt%, pouring the nanofiber dispersion liquid into a mold, pre-freezing at ultralow temperature, and performing freeze drying to obtain the polyamic acid nanofiber aerogel. (3) And (2) placing the polyamic acid nanofiber aerogel in a heating furnace, heating the polyamic acid nanofiber aerogel from room temperature to 150 ℃ at the heating rate of 2 ℃/min, and preserving heat for 0.5h, and then heating the polyamic acid nanofiber aerogel to 300 ℃ at the heating rate of 2 ℃/min and preserving heat for 0.5h to obtain the polyimide nanofiber aerogel. The aerogel had a density of 13.65mg/cm3The porosity was 99.34%, the shrinkage was 14.35%, the stress at 50% compressive strain was 30.62kPa, and the contact angle was 131.52 °.
Claims (11)
1. A polyimide nanofiber aerogel is characterized by comprising two or more polyimide fibers, wherein at least one of the polyimide fibers is a polyimide fiber which can be thermally fused under high-temperature thermal imidization treatment; the polyimide nanofiber aerogel is characterized in that melting cross-linking points are arranged among fibers; the content of the polyimide fiber thermally meltable under high-temperature thermal imidization treatment is 10 to 50 wt%, preferably 12 to 30 wt%.
2. The polyimide nanofiber aerogel according to claim 1, wherein the diameter of the polyimide nanofiber is 100-1000nm, preferably 200-700 nm.
3. The polyimide nanofiber aerogel according to claim 1, wherein the density of the polyimide nanofiber aerogel is 5-50 mg/cm3。
4. The polyimide nanofiber aerogel according to claim 1, wherein the water contact angle of the polyimide nanofiber aerogel is 125 ° to 140 °.
5. The polyimide nanofiber aerogel according to claim 1, wherein the polyimide nanofiber aerogel has a porosity of 97% or more; the stress under the compressive strain 50 is 10 to 100 kPa.
6. The preparation method of the polyimide nanofiber aerogel according to claim 1, comprising the steps of:
a: synthesizing a polyamic acid solution;
b: preparing a polyamic acid solution into a polyamic acid nanofiber membrane through electrostatic spinning;
c: dispersing the polyamic acid nanofiber membrane in a solvent to prepare polyamic acid nanofiber dispersion liquid; wherein at least one polyamic acid nanofiber membrane contains polyamic acid fibers which can be thermally fused under high-temperature thermal imidization treatment;
d: freezing and crystallizing the dispersion liquid of more than two kinds of polyamide acid nano fibers to prepare a crystal phase of the dispersion liquid of the polyamide acid nano fibers; removing the crystalline phase of the polyamic acid nanofiber dispersion liquid through vacuum freeze drying to obtain the uncrosslinked polyamic acid nanofiber aerogel;
e: and performing high-temperature thermal imidization treatment on the polyamic acid nanofiber aerogel to obtain the micro-crosslinking polyimide nanofiber aerogel.
7. The method for preparing the polyimide nanofiber aerogel according to claim 6, wherein the solvent dispersed in the step C is one or more of ethylene glycol, glycerol, tert-butyl alcohol, water, dioxane and phenol; preferably pure tert-butyl alcohol or a 20-30 wt% tert-butyl alcohol aqueous solution.
8. The method for preparing the polyimide nanofiber aerogel according to claim 6, wherein the polyamic acid fiber thermally fusible under high temperature thermal imidization treatment is one or more selected from a polyamic acid fiber of a hexafluoro dianhydride (6FDA)/4,4 '-diaminodiphenyl ether (4, 4' -ODA) system, a polyamic acid fiber of a 3,3 ', 4, 4' -diphenyl ether tetracarboxylic dianhydride (ODPA)/4,4 '-ODA system, a polyamic acid fiber of a bisphenol A dianhydride (BPADA)/4, 4' -ODA system, a polyimide precursor fiber of P84 type, and a polyetherimide precursor fiber.
9. The preparation method of the polyimide nanofiber aerogel according to claim 6, wherein the frozen crystals in the step D are pre-frozen in a freeze dryer at a low temperature of-10 to-95 ℃, preferably at a low temperature of-20 to-90 ℃, and the freezing time is 2 to 15 hours, preferably 3 to 10 hours; or performing rapid freezing in the liquid nitrogen atmosphere, wherein the freezing time is 5-40 min, and preferably 10-20 min.
10. The preparation method of the polyimide nanofiber aerogel according to claim 6, wherein the high-temperature thermal imidization treatment in the step E is carried out by raising the temperature from room temperature to 130-160 ℃, preferably 135 ℃, and keeping the temperature for 0.1-2 h, preferably 0.3-1 h, and most preferably 0.5 h; then heating to 200-400 ℃, preferably 300-350 ℃, and preserving heat for 0.1-2 h, preferably 0.3-1 h, and most preferably 0.5 h; the heating rate is 1-5 ℃/min, preferably 2-3 ℃/min.
11. Polyimide nanofiber aerogels prepared according to claims 1-10 and articles thereof.
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